Operator Panel options grayed out
Try choosing File > Load Factory Settings. This will discard any customizations you've made to your settings. Your file will close and be replaced with the default scene, so any unsaved work will be lost. For this reason you should save your project before loading factory settings, and re-open it after doing so. If this solves your problem you can then save the reset (fixed) settings from the "Save User Settings" button at the bottom of the Preferences window so that you won't run into the problem again.

This solution was suggested on Blender Artists by user "mib2berlin" to a user experiencing the same issue. The issue is apparently not specific to the spiral options, but can happen with other tools that use the Operator Panel.